This invention relates generally to pipeline pigs that service a pipeline and move forward through the interior of the pipeline either by means of a tether or by the flow of pressurized gas or liquid. More specifically, this invention relates to pipeline pigs which are designed to scratch the interior surface of a pipeline to dislodge pits and other debris.
A wide variety of pipeline pigs for inspecting, servicing, and maintaining pipelines have been developed for use in the pipeline industry. One type of pipeline pig, commonly known as a “bristle pig,” is equipped with a set of wires or bristles on one end of the pig. Bristle pigs have been used for some time in the pipeline industry to scratch the interior surface of a pipeline to dislodge pits and other debris. Bristle pigs are typically moved through the pipeline either by pulling the pig through the pipeline or, more commonly, by forcing the pig to move forward in response to pipeline pressure or fluid flow. However, because of the orientation of the bristles—which extend radially upward and away from the leading end (or direction of travel) of the pig—bristle pigs are unidirectional. If the pig becomes stuck in the pipeline the bristles prevent the pig from being dislodged by pulling or propelling it in the opposite direction or reversing the direction of fluid flow. In many cases, the only means of removal is digging up a portion of the pipeline containing the stuck bristle pig and extracting the pig. Therefore, a need exists for a bidirectional bristle pig. Also, in some cases, a need exists for cleaning a portion of piping in a reciprocating fashion, that is, pulling or propelling the bristle pig in one direction and then the other.